TECHNICAL FIELD
[0001] The present invention relates to a head drive unit and an inkjet printer, and more
particularly to a head drive unit and an inkjet printer that can prevent an increase
in viscosity of an ink even when an inkjet head is present outside an image forming
region for a recording medium.
BACKGROUND
[0002] In an inkjet printer that forms an image by impacting minute droplets from nozzles
onto a recording medium, viscosity of an ink in the nozzles is increased when discharge
of the droplets is stopped for a small period of time alone, thereby leading to a
discharge failure in some situations.
[0003] In an actual printing operation, there are some nozzles that keep preventing discharge
of droplets depending on image data. In the prior art, a meniscus oscillation signal
used for oscillating a liquid surface at a nozzle tip (which will be referred to as
a meniscus hereinafter) is uniformly input to all nozzles before or after a discharge
signal that is output to an inkjet head in synchronization with a print timing signal.
As a result, in the prior art, the ink in the nozzles is caused to flow before or
after discharge of the droplets, and viscosity is thereby lowered to stabilize the
discharge. Further, in the prior art, the meniscus oscillation signal is applied even
to nozzles that do not discharge droplets in synchronization with the print timing
signal. As a result, an increase in viscosity of the ink in the nozzles is avoided
(Patent Documents 1 and 2).
PRIOR ART DOCUMENTS
PATENT DOCUMENTS
[0004]
Patent Document 1: Japanese Patent No. 3556794
Patent Document 2: Japanese Patent No. 4345346
SUMMARY OF THE INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
[0005] Some of inkjet printers include a head drive unit equipped with an inkjet head driven
based on a drive signal and a head drive apparatus that applies a discharge signal
to the inkjet head based on image data and a print timing signal input from the outside
and discharges droplets from nozzles to form an image on a recording medium as well
as a print control apparatus that outputs the image data and the print timing signal
to the head drive unit. To the print control apparatus are input the image data from
a printer control apparatus (a PC or the like) as an external apparatus that controls
the entire printer and a print trigger signal indicative of start of printing. The
print trigger signal is input from a carriage apparatus when the inkjet head reaches
an image forming region for the recording medium based on positional information of
the inkjet head in a recording medium width direction (a main scanning direction).
The print control apparatus generates the print timing signal in the image forming
region based on this print trigger signal and continuously outputs this signal.
[0006] In such a inkjet printer, in case of preventing an increase in viscosity of the ink
in the nozzles like the conventional technology, since the meniscus oscillation signal
for oscillating the meniscus is applied in synchronization with the print timing signal,
an increase in viscosity of the ink can be effectively avoided during printing on
the recording medium. However, during a period that the inkjet head is present outside
the image forming region between a scan that the inkjet head moves along the main
scanning direction crossing a carrying direction (a sub-scanning direction) of the
recording medium and a subsequent scan (a period for acceleration/deceleration, stop,
and reversal of a scan operation), since the image data is not present and the print
timing signal is not input from the print control apparatus, the meniscus oscillation
signal cannot be input, and hence an increase in viscosity of the ink in the nozzles
cannot be prevented outside this image forming region.
[0007] Furthermore, when an external printer control apparatus adds dummy image data that
is not printed to the end of image data corresponding to one scan operation, the meniscus
oscillation signal can be applied even if the inkjet head is present outside the image
forming region between scans. However, since the printer control apparatus does not
have means for acquiring a print trigger signal output from the carriage apparatus
that is another apparatus and timing to start subsequent print is unknown, it is difficult
to determine a level of dummy image data to be provided. Moreover, since excess data
that is the dummy image data is transmitted to the print control apparatus, there
occurs a problem that an actual transfer rate is lowered and a print throughput is
also decreased.
[0008] On the other hand, when the print control apparatus is set to transmit the dummy
image data to the head drive apparatus, it may be possible to realize application
of the meniscus oscillation signal even if the inkjet head is present outside the
image forming region. However, fundamentally, since the print control apparatus does
not have an image data generating function, unnecessary processing for generating
the dummy image data is added. Since the print control apparatus requires ultrahigh-speed
processing, e.g., data reception from an external apparatus (the printer control apparatus)
or storage of image data in a memory in the apparatus, if unnecessary processing is
added, a faster CPU or FPGA is required to meet demanded specifications, which results
in a great increase in cost.
[0009] Thus, it is an object of the present invention is to provide a head drive unit that
enables applying a meniscus oscillation signal and preventing an increase in viscosity
of an ink in a nozzle even when an inkjet head is present outside an image forming
region of a recording medium where a print timing signal is not acquired, and to provide
an inkjet printer including this head drive unit.
[0010] Further, the discharge failure problem caused due to an increase in viscosity of
the ink can be avoided by forcedly continuously discharging droplets from the nozzles.
However, in this case, since the print timing signal cannot be acquired when the inkjet
head is present outside the image forming region, a signal used for forcedly discharging
the droplets (which will be referred to as a flushing signal hereinafter) cannot be
applied to the inkjet head, and there is the same problem as that in case of the meniscus
oscillation signal.
[0011] Therefore, it is another object of the present invention to provide a head drive
unit that enables preventing an increase in viscosity of an ink in a nozzle by forcedly
discharge a droplet from the nozzle even when an inkjet head is present outside an
image forming region of a recording medium where a print timing signal cannot be acquired,
and to provide an inkjet printer including this head drive unit.
[0012] Furthermore, it is still another object of the present invention to provide a head
drive unit that enables preventing an increase in viscosity of an ink in a nozzle
by selecting either application of a meniscus oscillation signal or forced discharge
of a droplet from the nozzle even when an inkjet head is present outside an image
forming region of a recording medium where a print timing signal cannot be acquired,
and to provide an inkjet printer including this head drive unit.
[0013] Other objects of the present invention will become obvious from the following description.
MEANS FOR SOLVING PROBLEM
[0014] To realize at least one of the above-described objects, a head drive unit and an
inkjet printer reflecting one aspect of the present invention has the following.
[0015] A head drive unit comprising:
an inkjet head driven based on a drive signal; and
a head drive apparatus that outputs a discharge signal to the inkjet head based on
image data and a print timing signal that are input from an external apparatus, and
discharges a droplet from a nozzle to form an image on a recording medium,
wherein the head drive apparatus comprises:
a drive signal output unit for outputting either the discharge signal used for discharging
a droplet from the nozzle to form an image or a meniscus oscillation signal used for
an oscillating meniscus at a tips of the nozzle without discharging a droplet from
the nozzle as a drive signal to the inkjet head;
a cycle generation unit for generating a cyclic oscillation timing signal for the
meniscus oscillation signal;
an input interruption detection unit for detecting that no input is made and input
of the print timing signal is interrupted even though a preset time has elapsed by
monitoring input of the print timing signal; and
a drive signal selection unit for selecting the meniscus oscillation signal as the
drive signal output from the drive signal output unit and continuously applying the
meniscus oscillation signal to all the nozzles of the inkjet head in synchronization
with the oscillation timing signal when the input interruption detection unit detects
that input of the print timing signal has been interrupted.
[0016] A head drive unit comprising:
an inkjet head driven based on a drive signal; and
a head drive apparatus that outputs a discharge signal to the inkjet head based on
image data and a print timing signal that are input from an external apparatus, and
discharges a droplet from a nozzle to form an image on a recording medium,
wherein the head drive apparatus comprises:
a drive signal output unit for outputting either the discharge signal used for discharging
a droplet from the nozzle to form an image or a flushing signal used for forcedly
discharging a droplet from the nozzle without forming an image as a drive signal to
the inkjet head;
a cycle generation unit for generating a cyclic flushing timing signal for the flushing
signal;
an input interruption detection unit for detecting that no input is made and input
of the print timing signal is interrupted even though a preset time has elapsed by
monitoring input of the print timing signal; and
a drive signal selection unit for selecting the flushing signal as the drive signal
output from the drive signal output unit and continuously applying the flushing signal
to all the nozzles of the inkjet head in synchronization with the flushing timing
signal when the input interruption detection unit detects that input of the print
timing signal has been interrupted.
[0017] A head drive unit comprising:
an inkjet head driven based on a drive signal; and
a head drive apparatus that outputs a discharge signal to the inkjet head based on
image data and a print timing signal that are input from an external apparatus, and
discharges a droplet from a nozzle to form an image on a recording medium,
wherein the head drive apparatus comprises:
a drive signal output unit for outputting either the discharge signal used for discharging
a droplet from the nozzle to form an image or a meniscus oscillation signal for an
oscillating liquid surface at a tip of the nozzle without discharging a droplet from
the nozzle or a flushing signal used for forcedly discharging a droplet from the nozzle
without forming an image to the inkjet head;
a cycle generation unit for generating at least either a cyclic oscillation timing
signal for the meniscus oscillation signal or a cyclic flushing timing signal for
the flushing signal;
an input interruption detection unit for detecting that no input is made and input
of the print timing signal is interrupted even though a preset time has elapsed by
monitoring input of the print timing signal; and
a drive signal selection unit for selecting the meniscus oscillation signal or the
flushing signal as the drive signal output from the drive signal output unit and continuously
applying the selected signal to all the nozzles of the inkjet head in synchronization
with the oscillation timing signal or the flushing timing signal when the input interruption
detection unit detects that input of the print timing signal has been interrupted.
[0018] An inkjet printer comprising:
a head drive unit according to any one of the above-mentioned head drive units;
a recording medium carrying apparatus for carrying the recording medium in a sub-scanning
direction;
a head moving apparatus for moving the inkjet head in a main scanning direction crossing
a carrying direction of the recording medium;
a positional information detecting apparatus for detecting positional information
of the inkjet head relative to the recording medium; and
a print control apparatus that continuously outputs the image data and the print timing
signal to the head drive apparatus based on the positional information detected by
the positional information detecting apparatus only when the inkjet head is present
in an image forming region for the recording medium.
BRIEF DESCRIPTION OF DRAWINGS
[0019]
FIG. 1 is an overall structural view showing an inkjet system including an inkjet
printer;
FIG. 2 is a structural block diagram showing an example of the inkjet system including
the inkjet printer;
FIG. 3 is a view for explaining the inside and outside of image forming regions relative
to a recording medium;
FIG. 4 is a structural block diagram showing an example of a head drive apparatus;
FIG. 5(a) is a view showing an example of a discharge signal waveform, and (b) is
a view showing an example of a meniscus oscillation signal waveform;
FIG. 6 is a flowchart for explaining meniscus oscillation processing;
FIG. 7 is a timing chart for explaining the meniscus oscillation processing;
FIG. 8 is a structural block diagram of a head drive apparatus according to another
embodiment;
FIG. 9 is an overall structural view showing an example of an inkjet system including
an inkjet printer in case of performing flushing;
FIG. 10 is a structural block diagram showing an example of the head drive apparatus
in case of performing flushing;
FIG. 11 is a flowchart for explaining the flushing processing;
FIG. 12 is a structural block diagram showing an example of the head drive apparatus
in case of selecting meniscus oscillation and flushing; and
FIG. 13 is a flowchart for explaining processing of selecting meniscus oscillation
processing and flushing processing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] Embodiments according to the present invention will now be described with reference
to the drawings.
[0021] FIG. 1 is an overall structural view showing an example of an inkjet system including
an inkjet printer, and FIG. 2 is a structural block diagram thereof.
[0022] In the drawings, reference numeral 100 denotes an inkjet printer, and 200 designates
a printer control apparatus that is an external apparatus configured to control the
entire inkjet printer 100.
[0023] In the inkjet printer 100, reference numeral 1 denotes each inkjet head (which will
be simply referred to as a head hereinafter), and the inkjet heads 1 are mounted on
a common carriage 2 in such a manner that nozzle surfaces having nozzles that discharge
inks aligned thereon face the lower side in the drawing. Here, four heads that discharge
inks in different colors are exemplified. However, the number of the heads 1 does
not really matter. The carriage 2 is provided to be reciprocable along a main scanning
direction represented as X-X' in the drawing by non-illustrated head moving apparatus.
[0024] In the present invention, a configuration of the head 1 is not really matter, it
is arbitrary to adopt, e.g., a configuration that a piezoelectric element such as
a PZT is driven by applying a drive signal, a volume of an ink chamber is contracted,
and a pressure is provided to the ink to thereby discharge the ink from each nozzle
or a configuration that a heater is energized by applying a drive signal, the ink
is heated to generate air bubbles, and the ink in the ink chamber is discharged from
the nozzles by a rupture action of the air bubbles.
[0025] A recording medium P is arranged below the carriage 2 to face the nozzle surfaces
of the heads 1. The recording medium P is intermittently carried at a predetermined
velocity along a sub-scanning direction represented as Y in the drawing by a non-illustrated
recording medium carrying apparatus having, e.g., a carrying roller pair that holds
the recording medium P and rotates to perform carriage and a carrying belt that has
the recording medium P mounted thereon and carries it.
[0026] Head drive apparatuses 3 configured to drive the heads 1 are mounted on the carriage
2 in proximity to the respective heads 1. The heads 1 and the head drive apparatuses
3 constitute a head drive unit.
[0027] When image data, a print timing signal, or various kinds of control commands are
transmitted from a print control apparatus 4 formed of, e.g., a CPU or an FPGA provided
in the inkjet printer 100 through a signal line 4a, each head drive apparatus 3 outputs
a drive signal to each head 1 based on the image data, the print timing signal, and
the various kinds of control commands. Particulars of an internal structure of the
head drive apparatus 3 will be described later.
[0028] In FIG. 1, reference numeral 5 denotes a linear encoder, and it is arranged along
the main scanning direction. An encoder sensor 6 (see FIG. 2) is provided to the carriage
2, and continuous pulse signals are detected from the linear encoder 5 when the carriage
2 moves along the main scanning direction. The combination of the linear encoder 5
and the encoder sensor 6 is an example of positional information detecting apparatus
for detecting positional information of each head 1 relative to the recording medium
P. Each detected pulse signal is transmitted to a mechanical control apparatus 7 formed
of, e.g., the CPU or the FPGA provided in the inkjet printer 100 through a signal
line 7a. The mechanical control apparatus 7 acquires positional information of the
carriage 2 along the main scanning direction based on the pulse signal.
[0029] The mechanical control apparatus 7 controls reciprocation of the carriage 2 along
the main scanning direction and carriage of the recording medium P along the sub-scanning
direction. Each head 1 is driven and controlled by the head drive apparatus 3 based
on image data, a print timing signal, or various kinds of control commands transmitted
from the print control apparatus 4 during a period that the heads 1 are present in
an image forming region on the recording medium P in a process of the reciprocation
of the carriage 2 along the main scanning direction controlled by this mechanical
control apparatus 7, and each head 1 discharges droplets from the nozzles to form
an image on the recording medium P.
[0030] At the time of the reciprocation of the carriage 2 along the main scanning direction,
as shown in FIG. 3, the carriage 2 starts acceleration from the outside of the image
forming region on one side of the recording medium P, cuts across the image forming
region on the recording medium P at a fixed velocity, again reaches the outside of
the image forming region on the other side of the recording medium P, and then repeats
an operation of performing deceleration, stop, and reversal outside the image forming
region and again starting acceleration toward the inside of the image forming region.
The mechanical control apparatus 7 is configured to determine whether the carriage
2 has reached the image forming region from the outside of the image forming region
for the recording medium P from acquired positional information of the carriage 2
along the main scanning direction. Moreover, when the carriage 2 comes close to the
image forming region, the mechanical control apparatus 7 generates a print trigger
signal indicative of start of print and transmits it to the print control apparatus
4. The print control apparatus 4 generates the print timing signal upon reception
of the print trigger signal only when the carriage 2 is present in the image forming
region, and it transmits this signal to each head drive apparatus 3 together with
image data and any other various kinds of control commands.
[0031] The printer control apparatus 200 that is an external apparatus of the inkjet printer
100 is constituted of a PC. The printer control apparatus 200 holds image data and
transmits the image data and various kinds of control commands that control the entire
inkjet printer 100 to the print control apparatus 4.
[0032] FIG. 4 is a structural block diagram showing an example of the internal configuration
of the head drive apparatus 3.
[0033] The head drive apparatus 3 has a drive signal output unit 31 and a drive signal selection
unit 32. As represented by examples in FIG. 5, this head drive apparatus 3 can generate
a discharge signal (FIG. 5(a)) used for discharge a droplet from a nozzle to form
an image and a meniscus oscillation signal (FIG. 5 (b)) that has a lower peak value
than the discharge signal and is used for oscillating a meniscus at each nozzle tip
without discharging a droplet from the nozzle as a drive signal output to the head
1. The drive signal selection unit 32 has a discharge signal waveform data memory
321a that stores waveform data of the discharge signal and a meniscus oscillation
signal waveform data memory 321b that stores waveform data of the meniscus oscillation
signal. The discharge signal waveform data in the discharge signal waveform data memory
321a and the meniscus oscillation signal waveform data in the meniscus oscillation
signal waveform data memory 321b are output to the drive signal output unit 31.
[0034] The drive signal output unit 31 has a control unit 311 that outputs a head control
signal to each head 1, a drive signal generation unit 312 that is controlled by the
control unit 311 and outputs a drive signal to the head 1, and a waveform switch unit
313 that is controlled by the control unit 311 and switches a drive signal waveform
that is output to the drive signal generation unit 312 to either a discharge signal
waveform from the discharge signal waveform data memory 321a of the drive signal selection
unit 32 or a meniscus oscillation signal waveform from the meniscus oscillation signal
waveform data memory 321b.
[0035] The control unit 311 controls the waveform switch unit 313 based on a discharge signal
request signal or a meniscus oscillation signal request signal output from the drive
signal selection unit 32 and switches a drive signal applied to the head 1 to either
the discharge signal or the meniscus oscillation signal. Image data and the print
timing signal are input to this control unit 311 from the print control apparatus
4. At the time of normal image formation that the carriage 2 is present in the image
forming region, the control unit 311 outputs the discharge signal to each head 1 from
the drive signal generation unit 312 based on the image data and the print timing
signal. As a result, droplets are discharged from the nozzles, and image formation
is carried out.
[0036] It is to be noted that each of the discharge signal shown in FIG. 5 (a) and the meniscus
oscillation signal shown in FIG. 5(b) is an example and can be appropriately set in
accordance with the configuration of the head 1.
[0037] The drive signal selection unit 32 determines which one of the discharge signal and
the meniscus oscillation signal is selected as a drive signal output from the drive
signal output unit 31 to the head 1 with respect to the control unit 311 of the drive
signal output unit 31. The drive signal selection unit 32 has a discharge signal request
unit 322 that outputs a discharge signal request signal to the control unit 311 of
the drive signal output unit 31 and a meniscus oscillation signal request unit 323
that outputs a meniscus oscillation signal request signal to the control unit 311.
[0038] Upon inputting a print request signal for performing normal image formation that
is transmitted from the print control apparatus 4 when the carriage 2 is present within
the image forming region, the discharge signal request unit 322 outputs the discharge
signal request signal to the control unit 311 of the drive signal output unit 31.
On the other hand, when the carriage 2 is present outside the image forming region,
the meniscus oscillation signal request unit 323 outputs the meniscus oscillation
signal request signal to the control unit 311 of the drive signal output unit 31.
[0039] Here, to detect that the carriage 2 is present outside the image forming region,
the drive signal selection unit 32 has the following configuration.
[0040] The print timing signal that is continuously output from the print control apparatus
4 is also input to the drive signal selection unit 32. An interrupted time measurement
unit 324 that monitors cyclic input of the continuous print timing signal is provided
to the drive signal selection unit 32.
[0041] The interrupted time measurement unit 324 measures an interrupted time during which
no print timing signal is input from input of one (corresponding to one pulse) print
timing signal to input of a subsequent (corresponding to one pulse) print timing signal,
and outputs a measured value to a time comparison unit 325. The time comparison unit
325 compares this interrupted time with a set time previously set in a time set unit
325a. This set time is set to a time that is sufficient to estimate that the print
timing signal is interrupted by movement of the carriage 2 to the outside of the image
forming region. Further, when the measured value exceeds the set time as a result
of comparison between the measured value and the set time, the time comparison unit
325 outputs a signal indicating that the set time has elapsed, i.e., a signal indicating
that the carriage 2 is present outside the image forming region to the meniscus oscillation
signal request unit 323.
[0042] It is to be noted that the interrupted time measurement unit 324, the time comparison
unit 325 and the time set unit 325a of the drive signal selection unit 32 constitute
input interruption detection unit.
[0043] When this signal has been input, the meniscus oscillation signal request unit 323
outputs the meniscus oscillation signal request signal to the control unit 311 of
the drive signal output unit 31 and also outputs the signal to a cycle generation
unit 326.
[0044] The cycle generation unit 326 is a cycle generate unit for generating an oscillation
timing signal as a cycle signal used for continuously outputting the meniscus oscillation
signal shown in FIG. 5(b) upon receiving the signal from the meniscus oscillation
signal request unit 323. The cycle generation unit 326 outputs this oscillation timing
signal to the control unit 311 of the drive signal output unit 31.
[0045] The carriage 2 that has reached the outside of the image forming region from the
inside of the image forming region then turns around and again enters the image forming
region. The drive signal selection unit 32 has the following configuration to detect
that the carriage 2 again enters the image forming region.
[0046] A time measurement unit 327 for measuring a duration time of the oscillation timing
signal output from the cycle generation unit 326 is provided in the drive signal selection
unit 32. The duration time measured by the time measurement unit 327 is output to
a time comparison unit 328. The time comparison unit 328 compares a measured value
of this duration time with a set time previously set in the time set unit 328a. This
set time is set to a time that is sufficient to estimate that the carriage 2 has reached
a point just before again coming near to the image forming region. Additionally, when
a measured value exceeds the set time as a result of comparing the measured value
and the set time, the time comparison unit 328 outputs a signal indicating that the
set time has elapsed, i.e., a signal indicating that the carriage 2 has come near
to the image forming region to the discharge signal request unit 322 to restart image
formation.
[0047] When this signal has been input, the discharge signal request unit 322 outputs the
discharge signal request signal to the control unit 311 of the drive signal output
unit 31, outputs a stop request signal to the cycle generation unit 326, and terminates
the output of the oscillation timing signal. As a result, the output of the meniscus
oscillation signal to each head 1 is terminated.
[0048] It is to be noted that the time measurement unit 327, the time comparison unit 328
and the time set unit 328a of the drive signal selection unit 32 constitute a meniscus
oscillation signal termination unit.
[0049] A specific flow of meniscus oscillation processing executed by the inkjet printer
100 will now be described with reference to a flowchart shown in FIG. 6 and a timing
chart shown in FIG. 7.
[0050] The print control apparatus 4 outputs a discharge print request signal for effecting
normal image formation to the head drive apparatus 3 and starts a print operation.
Then, the carriage 2 having the heads 1 mounted thereon moves on the recording medium
P along the main scanning direction. When the carriage 2 comes near to the image forming
region, a print trigger signal is output to the print control apparatus 4 from the
mechanical control apparatus 7 based on positional information detected and acquired
by the encoder sensor 6. Upon inputting this print trigger signal, the print control
apparatus 4 continuously outputs the print timing signal to each head drive apparatus
3. As a result, the head drive apparatus 3 discharges droplets from the nozzles of
each head 1 based on the print timing signal and the image data from the print control
apparatus 4 and forms an image corresponding to one line on the recording medium P
along the main scanning direction.
[0051] When the carriage 2 has moved to the outside of the image forming region, since data
of an image that should be formed in this one line is no longer present, the print
timing signal from the print control apparatus 4 is interrupted. In the drive signal
selection unit 32 in each head drive apparatus 3, the interrupted time measurement
unit 324 keeps measuring an interrupted time of the print timing signal that is continuously
output from the print control apparatus 4 (S1, S2). Furthermore, when the time comparison
unit 325 detects that an interrupted time of this print timing signal exceeds a set
time that has been set in advance (in case of Yes at S2), the time comparison unit
325 outputs a meniscus oscillation signal request signal to the control unit 311 of
the drive signal output unit 31 from the meniscus oscillation signal request unit
323 and also outputs a cyclic oscillation timing signal to the control unit 311 from
the cycle generation unit 326.
[0052] When the control unit 311 receives the meniscus oscillation signal request signal,
the drive signal output unit 31 controls the waveform switch unit 313, and switches
a drive signal, which is output from the drive signal generation unit 312 to each
head 1, to the meniscus oscillation signal. Then, the drive signal output unit 31
continuously outputs the meniscus oscillation signal to all the nozzles of each head
1 in synchronization with the oscillation timing signal and oscillates meniscuses
of all the nozzles (S3).
[0053] A state that the print timing signal is not input from the print control apparatus
4 continues while this oscillation timing signal is cyclically output (in case of
No at S4). The drive signal selection unit 32 keeps measuring a duration time of output
of the oscillation timing signal in the time measurement unit 327 (S5). Furthermore,
when the time comparison unit 328 detects that the duration time of this oscillation
timing signal exceeds a set time that has been previously set (in case of Yes at S5),
the drive signal selection unit 32 outputs a discharge signal request signal to the
control unit 311 of the drive signal output unit 31 from the discharge signal request
unit 322 and outputs a stop request signal to the meniscus oscillation signal cycle
generation unit 326. As a result, the output of the oscillation timing signal is stopped
(S6).
[0054] It is to be noted that, here, if input of the print timing signal has been detected
after output of the oscillation timing signal and before elapse of the set time (Yes
at S4), the drive signal selection unit 32 likewise outputs the stop request signal
to the meniscus oscillation signal cycle generation unit 326 and stops the oscillation
timing signal.
[0055] Then, when the carriage 2 again moves close to the image forming region to form an
image corresponding to a next line, the print trigger signal is again output to the
print control apparatus 4 from the mechanical control apparatus 7 based on positional
information detected and acquired by the encoder sensor 6, droplets are likewise discharged
from the nozzles of each head 1, and the image corresponding to one line is formed
along the main scanning direction.
[0056] According to this head drive unit (the heads 1 and the head drive apparatuses 3)
and the inkjet printer 100 including this unit, even when the heads 1 are present
outside the image forming region of the recording medium P where the print timing
signal is not acquired, the meniscus oscillation signal can be generated in each head
drive apparatus 3 and output to each head 1, and meniscuses of all the nozzles can
be oscillated to avoid an increase in viscosity of the inks in the nozzles. Since
each head drive apparatus 3 is fundamentally a portion that controls the drive signal
output to each head 1, the meniscus oscillation signal can be output to all the nozzles
of the head 1 irrespective of image data. As a result, a considerable circuit change
or addition of complicated processing is not required.
[0057] Moreover, according to this head drive unit and the inkjet printer 100, when the
drive signal selection unit 32 measures a time during which output of the meniscus
oscillation signal continues and detects that the duration time exceeds a preset time,
the meniscus oscillation signal is stopped, the drive signal is switched to the discharge
signal, and hence each head drive apparatus 3 can automatically oscillate the meniscus
between scans in the main scanning direction. Therefore, the meniscuses of all the
nozzles can be oscillated when the carriage 2 is present outside the image forming
region without imposing a burden on the print control apparatus 4 or a host external
apparatus (the printer control apparatus 200), thereby stabilizing discharge.
[0058] In the above-described embodiment, the meniscus oscillation signal termination unit
measures a duration time of the cyclic oscillation timing signal continuously output
from the cycle generation unit 326 with the use of the time measurement unit 327,
the number of times of outputting of the respective oscillation timing signals may
be measured.
[0059] FIG. 8 shows this embodiment. A number-of-time measurement unit 327' for measuring
the number of times of outputting the oscillation timing signal is provided to the
meniscus oscillation signal termination unit. The number-of-time measurement unit
327' is configured to output a measured value of the number of times of outputting
the oscillation timing signal to a number-of-time comparison unit 328'. The number-of-time
comparison unit 328' compares this measured value of the number of times of output
with a set number of times that has been previously set in a number-of-time set unit
328a'. This set number of times is set to the number of times that is sufficient to
estimate that the carriage 2 has reached a point just before again coming close to
the image forming region. Additionally, when the number-of-time comparison unit 328'
detects that the measured value has reached the set number of times, it outputs a
signal indicating that output has been made for the set number of times, i.e., a signal
indicating that the carriage 2 comes close to the image forming region to the discharge
signal request unit 322 to restart image formation.
[0060] According to this embodiment, it is possible to provide the same effect as that in
case of measuring a duration time of output of the oscillation timing signal.
[0061] FIG. 9 is an overall structural view showing an example of an inkjet printer system
including an inkjet printer 100' according to another embodiment to avoid an increase
in viscosity of inks in nozzles, and FIG. 10 shows an example of an internal configuration
of a head drive apparatus 3 in the inkjet printer 100'. Since portions denoted by
the same reference numerals as those in FIG. 1 and FIG. 4 represent portions having
the same structures, explanation thereof will be used, and a description here will
be omitted.
[0062] An ink receiver 8 configured to receive droplets forcedly discharged from each head
1 is arranged outside an image forming regions on both sides of a recording medium
P in this inkjet printer 100'.
[0063] Each head drive apparatus 3 can generate a discharge signal used for discharging
droplets from nozzles to perform image formation and a flushing signal used for forcedly
discharging droplets from the nozzles without performing image formation as drive
signals that are output to each head 1. This head drive apparatus 3 has a discharge
signal waveform data memory 321a that stores waveform data of the discharge signal
and a flushing signal waveform data memory 321c that stores waveform data of the flushing
signal in a head drive signal selection unit 32.
[0064] Therefore, when a waveform switch unit 313 of a drive signal output unit 31 is controlled
by a control unit 311, it switches the drive signal that is to be output to a drive
signal generation unit 312 to either a discharge signal waveform that is output from
the discharge signal waveform data memory 321a of the drive signal selection unit
32 or a flushing signal waveform that is output from the flushing signal waveform
data memory 321c.
[0065] The flushing signal waveform that is stored in this flushing signal waveform data
memory 321c is arbitrary as long as it enables forcedly discharging droplets from
the nozzles, and it can be appropriately set in accordance with a structure of each
head 1. Here, a description will be given as to an illustrative example of the flushing
signal waveform having a signal waveform different from the discharge signal waveform.
However, as to the flushing signal waveform, a signal having the same waveform as
the discharge signal waveform may be used. When the flushing signal waveform is the
same as the discharge signal waveform, the flushing signal waveform data memory 321c
and the waveform switch unit 313 may be eliminated. In this case, it is good enough
to configure the discharge signal waveform stored in the discharge signal waveform
data memory 321a to be output to the dive signal generation unit 312.
[0066] The drive signal selection unit 32 determines which one of the discharge signal and
the flushing signal corresponds to the drive signal applied from the drive signal
output unit 31 to each head 1 with respect to the control unit 311 of the drive signal
output unit 31. Therefore, the drive signal selection unit 32 has a flushing signal
request unit 323' that transmits a flushing signal request signal to the control unit
311 when the carriage 2 is present outside the image forming region. The flushing
signal request unit 323' outputs a signal indicating that a set time has elapsed,
i.e., a signal indicating that the carriage 2 is present outside the image forming
region from a time comparison unit 325.
[0067] When a signal has been input from the time comparison unit 325, the flushing signal
request unit 323' outputs a flushing signal request signal to the control unit 311
of the drive signal output unit 31 and also outputs a signal to a cycle generation
unit 326.
[0068] Upon receiving a signal from the flushing signal request unit 323' , the cycle generation
unit 326 generates a cycle for making flushing signals continuous and outputs it as
a flushing timing signal to the control unit 311 of the drive signal output unit 31.
As a result, when the carriage 2 is present outside the image forming region, droplets
from all the nozzles are forcedly discharged to the ink receiver 8.
[0069] A time measurement unit 327 measures a duration time of output of the flushing timing
signal from the cycle generation unit 326, outputs a signal indicating that a set
time has elapsed to a discharge signal request unit 322 like the example of the oscillation
timing signal, and terminates output of the flushing signal.
[0070] A specific flow of meniscus oscillation processing executed by this inkjet printer
100' will now be described with reference to a flowchart shown in FIG. 11.
[0071] A print control apparatus 4 outputs a discharge print request signal for effecting
normal image formation to each head drive apparatus 3 and starts a print operation.
Then, the carriage 2 having the heads 1 mounted thereon moves on a recording medium
P along a main scanning direction. When the carriage 2 comes near to the image forming
region, a print trigger signal is output to the print control apparatus 4 from a mechanical
control apparatus 7 based on positional information detected and acquired by an encoder
sensor 6. Upon inputting this print trigger signal, the print control apparatus 4
continuously outputs the print timing signal to each head drive apparatus 3. As a
result, the head drive apparatus 3 discharges droplets from the nozzles of each head
1 based on the print timing signal and image data from the print control apparatus
4 and forms an image corresponding to one line on the recording medium P along the
main scanning direction.
[0072] When the carriage 2 has moved to the outside of the image forming region, since data
of an image that should be formed in this one line is no longer present, the print
timing signal from the print control apparatus 4 is interrupted. In the drive signal
selection unit 32 in each head drive apparatus 3, an interrupted time measurement
unit 324 keeps measuring an interrupted time of the print timing signal that is continuously
output from the print control apparatus 4 (S10, S11). Furthermore, upon detecting
that an interrupted time of this print timing signal exceeds a set time that has been
set in advance (in case of Yes at S11), the drive signal selection unit 32 outputs
a flushing signal request signal to the control unit 311 of the drive signal output
unit 31 from the flushing signal request unit 323' and also outputs a cyclic flushing
timing signal to the control unit 311 from the cycle generation unit 326.
[0073] When the control unit 311 receives the flushing signal request signal, the drive
signal output unit 31 controls the waveform switch unit 313, and switches a drive
signal, which is output from the drive signal generation unit 312 to each head 1,
to the flushing signal. Then, the drive signal output unit 31 continuously outputs
the flushing signal to all the nozzles of each head 1 in synchronization with the
flushing timing signal and forcedly discharges droplets from all the nozzles (S12).
[0074] A state that the print timing signal is not input from the print control apparatus
4 continues while the flushing timing signal is cyclically output (in case of No at
S13). The drive signal selection unit 32 keeps measuring a duration time of output
of the flushing timing signal in the time measurement unit 327 (S14). Upon detecting
that the duration time of this flushing timing signal has exceeded a set time that
has been previously set (in case of Yes at S14), the drive signal selection unit 32
outputs a discharge signal request signal to the control unit 311 of the drive signal
output unit 31 from the discharge signal request unit 322 and outputs a stop request
signal to the cycle generation unit 326. As a result, the output of the flushing timing
signal is stopped (S15).
[0075] It is to be noted that, here, if input of the print timing signal is detected after
output of the flushing timing signal and before elapse of the set time (Yes at S13),
the drive signal selection unit 32 likewise outputs the stop request signal to the
cycle generation unit 326 and stops the flushing timing signal.
[0076] Then, when the carriage 2 again moves close to the image forming region to form an
image corresponding to next one line, the print trigger signal is again output to
the print control apparatus 4 from the mechanical control apparatus 7 based on positional
information detected and acquired by the encoder sensor 6. Further, like the above
example, droplets are discharged from the nozzles of each head 1, and the image corresponding
to one line is formed along the main scanning direction.
[0077] Even if the flushing signal is used in place of the meniscus oscillation signal,
droplets can be forcedly discharged when the carriage 2 is present outside the image
forming region, and an increase in viscosity of inks in the nozzles can be avoided
like the example of using meniscus oscillation signal.
[0078] The embodiment of using the above-described meniscus oscillation signal as means
for avoiding an increase in viscosity of inks in the nozzles when the carriage 2 is
present outside the image forming region may be combined with the embodiment of using
the flushing signal to select both the signals. This embodiment will now be described
hereinafter.
[0079] Since an overall configuration of the inkjet head printer system that selects the
meniscus oscillation signal and the flushing signal is the same as that in FIG. 9,
FIG. 12 show an example of an internal configuration of the head drive apparatus 3
alone. Since portions designated by the same reference numerals as those in FIG. 4
and FIG. 10 represent portions having the same configurations, explanation thereof
will be used, a description here will be omitted.
[0080] In this embodiment, the drive signal selection unit 32 has a discharge signal waveform
data memory 321a that outputs a discharge signal waveform to the drive signal output
unit 31, a meniscus oscillation signal waveform data memory 321b that outputs a meniscus
oscillation signal waveform, and a flushing signal waveform data memory 321c that
outputs a flushing signal waveform.
[0081] Further, the drive signal selection unit 32 outputs a detection signal indicating
detection of input interruption of the print timing signal in a time comparison unit
325 to the meniscus oscillation signal request unit 323 and the flushing signal request
unit 323'. Upon receiving this signal, each of the meniscus oscillation signal request
unit 323 and the flushing signal request unit 323' outputs a meniscus oscillation
signal request signal and a flushing signal request signal to a selection unit 329,
respectively.
[0082] The selection unit 329 is selecting means for selecting one of the meniscus oscillation
signal request signal and the flushing signal request signal input thereto as a signal
that is output to the control unit 311 of the drive signal output unit 31. The selection
unit 329 outputs the selected meniscus oscillation signal request signal or flushing
signal request signal to the control unit 311 and also outputs the selected signal
to the cycle generation unit 326.
[0083] Usually, since flushing involves consumption of the inks, it is preferable to set
the selection unit 329 so that it can preferentially select the meniscus oscillation
signal that does not involve the consumption of the inks at the time of selecting
the meniscus oscillation signal or the flushing signal when the carriage 2 is present
outside the image forming region. As a result, the consumption of the inks involved
by the flushing can be suppressed.
[0084] A selecting operation of the selection unit 329 may be carried out by, e.g., manipulating
a switch button by an operator, or the meniscus oscillation signal or the flushing
signal may be switched in accordance with a preset order. However, as shown in FIG.
12, it is preferable to provide a counting unit 329a for counting the number of times
of selecting the meniscus oscillation signal by the selection unit 329 to the drive
signal selection unit 32, thereby switching the signals based on a counted value provided
by this counting unit 329a.
[0085] The counting unit 329a counts the number of times of selecting the meniscus oscillation
signal by the selection unit 329 and compares it with a set value (e.g., 10 times)
that has been previously set. Furthermore, when the counted value that is the number
of times of selecting the meniscus oscillation signal has reached the set value, a
signal indicative of this state is output to the selection unit 329. Upon receiving
this signal, the selection unit 329 selects the flushing signal when the carriage
2 subsequently reaches the outside of the image forming region, and it forcedly discharges
droplets to the ink receiver 8.
[0086] A specific flow of meniscus oscillation and flushing processing executed by this
inkjet printer will now be described with reference to a flowchart shown in FIG. 13.
[0087] Here, a description will be given as to a flow when the selection unit 329 preferentially
selects the meniscus oscillation signal request signal and the counting unit 329a
counts the selected number of times.
[0088] The print control apparatus 4 outputs a discharge print request signal used for performing
normal image formation to each head drive apparatus 3 and starts a print operation.
Then, the carriage 2 having the heads 1 mounted thereon moves on the recording medium
P along the main scanning direction. When the carriage 2 comes near to the image forming
region, a print trigger signal is output to the print control apparatus 4 from the
mechanical control apparatus 7 based on positional information detected and acquired
by the encoder sensor 6. Upon inputting this print trigger signal, the print control
apparatus 4 continuously outputs the print timing signal to each head drive apparatus
3. As a result, the head drive apparatus 3 discharges droplets from the nozzles of
each head 1 based on the print timing signal and the image data from the print control
apparatus 4 and forms an image corresponding to one line on the recording medium P
along the main scanning direction.
[0089] When the carriage 2 has moved to the outside of the image forming region, since data
of an image that should be formed in this one line is no longer present, the print
timing signal from the print control apparatus 4 is interrupted. In the drive signal
selection unit 32 in each head drive apparatus 3, the interrupted time measurement
unit 324 keeps measuring an interrupted time of the print timing signal that is continuously
output from the print control apparatus 4 (S20, S21). Furthermore, upon detecting
that the interrupted time of this print timing signal exceeds a set time that has
been previously set (in case of Yes at S21), the drive signal selection unit 32 determines
whether the number of times of selecting the meniscus oscillation signal request signal
counted by the counting unit 329a has reached a set value that has been set in advance
(S22).
[0090] When it is determined that the counted value provided by the counting unit 329a has
not reached the set value (in case of No at S22), the selection unit 329 outputs the
meniscus oscillation signal request signal from the meniscus oscillation signal request
unit 323 to the control unit 311 of the drive signal output unit 31 and also outputs
a cyclic oscillation timing signal to the control unit 311 from the cyclic generation
unit 326.
[0091] When the control unit 311 receives the meniscus oscillation signal request signal,
the drive signal output unit 31 controls the waveform switch unit 313, and switches
a drive signal, which is output from the drive signal generation unit 312 to each
head 1, to the meniscus oscillation signal. Then, the drive signal output unit 31
continuously outputs the meniscus oscillation signal to all the nozzles of each head
1 in synchronization with the oscillation timing signal and oscillates meniscuses
of all the nozzles (S23).
[0092] The counting unit 329a increments the counted value by 1 every time the meniscus
oscillation signal request signal is selected by the selection unit 329 (S24).
[0093] Then, a state that the print timing signal is not input from the print control apparatus
4 continues (in case of No at S4). The drive signal selection unit 32 keeps measuring
a duration time of output of the oscillation timing signal in the time measurement
unit 327 (S26). Furthermore, when the time comparison unit 328 detects that the duration
time of this oscillation timing signal has exceeded a set time that has been previously
set (in case of Yes at S26), the drive signal selection unit 32 outputs a discharge
signal request signal to the control unit 311 of the drive signal output unit 31 from
the discharge signal request unit 322 and outputs a stop request signal to the meniscus
oscillation signal cycle generation unit 326. As a result, the output of the oscillation
timing signal is stopped (S27).
[0094] On the other hand, if it is determined that the counted value provided by the counting
unit 329a has reached the set value (in case of Yes at S22), the selection unit 329
switches the flushing signal request signal from the flushing signal request unit
323' to be output to the control unit 311 of the drive signal output unit 31 and outputs
the cyclic flushing timing signal to the control unit 311 from the cycle generation
unit 326. At this time, the counted value of the counting unit 329a is cleared.
[0095] When the control unit 311 receives the flushing signal request signal, the drive
signal output unit 31 controls the waveform switch unit 313, and switches a drive
signal, which is output from the drive signal generation unit 312 to each head 1,
to the flushing signal. Then, the drive signal output unit 31 continuously outputs
the flushing signal to all the nozzles of each head 1 in synchronization with the
flushing timing signal and forcedly discharges droplets from all the nozzles (S28).
[0096] A state that the print timing signal is not input from the print control apparatus
4 continues while this flushing timing signal is cyclically output (in case of No
at S29). The drive signal selection unit 32 keeps measuring a duration time of output
of the flushing timing signal in the time measurement unit 327. Furthermore, upon
detecting that the duration time exceeds a set time that has been previously set (in
case of Yes at S29), the drive signal selection unit 32 outputs a discharge signal
request signal to the control unit 311 of the drive signal output unit 31 from the
discharge signal request unit 322 and outputs a stop request signal to the cycle generation
unit 326. As a result, the output of the flushing signal is stopped (S30).
[0097] As a result, even if the carriage 2 is present outside the image forming region,
selecting either the meniscus oscillation signal or the flushing signal enables preventing
an increase in viscosity of the inks in the nozzles.
[0098] Since the selection unit 329 preferentially selects the meniscus oscillation, consumption
of the inks involved by the flushing can be suppressed. Moreover, when the number
of times of selecting the meniscus oscillation signal has reached a predetermined
number of times, the selection unit 329 automatically switches the signal to the flushing
signal, and hence an increase in viscosity of the inks can be suppressed by forced
discharge of droplets even though suppressing an increase in viscosity of the inks
by the meniscus oscillation alone is difficult, thereby effectively recovering the
nozzles.
[0099] In the head drive apparatus 3 shown in FIG. 12, the meniscus oscillation signal/flushing
termination unit has the time measurement unit 327, the time comparison unit 328,
and the time set unit 328a like FIG. 4. However, in the head drive apparatus 3, a
number-of-time measurement unit 327', a number-of-time comparison unit 328', and a
number-of-time set unit 328' that are the same as those in FIG. 8 may be provided
in place of the time measurement unit 327, the time comparison unit 328, and the time
set unit 328a so that the number of times of outputting the oscillation timing signal
or the flushing timing signal can be measured.
[0100] It is to be noted that, in each foregoing embodiment, like the prior art, when the
carriage 2 is present in the image forming region, the meniscus in each nozzle may
be oscillated by interposing the meniscus oscillation signal before or after the print
timing signal.
EXPLANATION OF LETTERS OR NUMERALS
[0101]
- 100, 100':
- inkjet printer
- 1:
- inkjet head
- 2:
- carriage
- 3:
- head drive apparatus
31: drive signal output unit
311: control unit
312: drive signal generation unit
313: waveform switch unit
32: drive signal selection unit
321a: discharge signal waveform data memory
321b: meniscus oscillation signal waveform data memory
321c: flushing signal waveform data memory
322: discharge signal request unit
323: meniscus oscillation signal request unit
323': flushing signal request unit
324: interrupted time measurement unit
325: time comparison unit
325a: time set unit
326: cycle generation unit
327: time measurement unit
327': number-of-time measurement unit
328: time comparison unit
328': number-of-time comparison unit
328a: time set unit
328a': number-of-time set unit
329: selection unit
329a: counting unit
- 4:
- print control apparatus
4a: signal line
- 5:
- linear encoder
- 6:
- encoder sensor
- 7:
- mechanical control apparatus
7a: signal line
- 8:
- ink receiver
- 200:
- printer control apparatus (external apparatus)
200a: signal line